Organically modified fine particles

ABSTRACT

A technique for bonding an organic group with the surface of fine particles such as nanoparticles through strong linkage is provided, whereas such fine particles are attracting attention as materials essential for development of high-tech products because of various unique excellent characteristics and functions thereof. Organically modified metal oxide fine particles can be obtained by adapting high-temperature, high-pressure water as a reaction field to bond an organic matter with the surface of metal oxide fine particles through strong linkage. The use of the same condition enables not only the formation of metal oxide fine particles but also the organic modification of the formed fine particles. The resulting organically modified metal oxide fine particles exhibit excellent properties, characteristics and functions.

CROSS REFERENCE TO RELATED APPLICATIONS

The subject application is a divisional application of U.S. patentapplication Ser. No. 13/535,103, filed Jun. 27, 2012, which in turn is adivisional of U.S. patent application Ser. No. 12/510,175, filed Jul.27, 2009, now U.S. Pat. No. 8,257,679, which in turn is a divisional ofU.S. patent application Ser. No. 11/173,348, filed Jul. 1, 2005, nowU.S. Pat. No. 7,803,347, the contents of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to organically modified fine particleshaving hydrocarbon strongly bound to the surface of fine particles,particularly, organically modified metal oxide fine particles, a processfor producing the same, and further a recovery or collection method offine particles such as nanoparticles, and applied techniques thereof.

Description of the Related Art

Fine particles, particularly, particles of nanometer size(nanoparticles) are expected to realize a technology satisfying requestsof a higher precision, a smaller size and a lighter weight than in thecurrent condition for all materials and products because of a variety ofunique excellent properties, characteristics and functions thereof.Therefore, nanoparticles are attracting attentions as a materialenabling the higher function, higher performance, higher density, andhigher preciseness of industrial materials, pharmaceutical and cosmeticmaterials and the like such as ceramic nano-structure modified material,optical functional coating material, electromagnetic shielding material,secondary battery material, fluorescent material, electronic partmaterial, magnetic recording material, and abrasive material, and alsoas a 21st century material. There is a lot of attention from theindustrial world being given thereto, because a series of discoveriessuch as onset of extra-high functionalities or new physical propertiesby the quantum size effect of the nanoparticles, and syntheses of newmaterials have been made in the recent basic researches for thenanoparticles. However, practical application of the nanoparticlesrequires addition of unique functions to the respective fine particles,and to that end, establishment of a technique for modifying the surfaceof particles is desired for enabling the addition of the functions.Organic modification is convenient for adding stably usable andapplicable functions to fine particles, particularly nanoparticles, anda modification through strong bond is particularly demanded.

Many reports for organic/inorganic composite materials and synthesesthereof have been disclosed up to now, and researches for organicmodification of inorganic particles have been also made, each of whichintended to carry out a reaction in an organic solvent for the organicmodification. A technique for reacting an organic material with fineparticles in a reaction field or water while synthesizing the particlesin water or an aqueous solution is not known. For the surfacemodification of particles, many techniques for modifying the surface ofinorganic particles in an organic solvent are known. However, particlesof nano-size are easy to coagulate, and a pretreatment such as use of asurface active agent is particularly needed for dispersing the particlessynthesized in water to an organic solvent. As mentioned above, noreport has been made for the technique for modifying the surface ofparticles while synthesizing the particles in water.

As a method for in-situ surface modification, reversed micelle method,hot soap method, and the like have been reported. In the reversedmicelle method, water is suspended to an oil phase by use of a surfaceactive agent to generate a reversed micelle, and a reactive substrate isadded thereto to reactively crystallize it. The metal oxide particlesgenerated in the suspended water phase are stabilized by the surfaceactive agent to stably disperse nanoparticles, in which the surfaceactive agent is in a state adsorbed by the particle surface without alinkage by reaction. In the hot soap method, the above method isperformed at high temperature by use of only the surface active agentwithout oil phase. This method is a technique using the effect that anaqueous solution of metal salt to be reacted is rapidly supplied withstirring and reactively crystallized, while the circumferential surfaceactive agent is adsorbed thereto. The cases reported up to now for theorganic modification involve adsorption of alkanethiol, but not reactivemodification.

There are frequently reported that high-temperature, high-pressure waterforms a homogeneous phase also with an organic material, and waterfunctions as an acid or basic catalyst in a high-temperature,high-pressure field to progress an organic synthetic reaction even underno catalyst. However, no method for a reaction between an inorganicmaterial and an organic material is reported.

It is known that highly crystalline particles of nano-size can besynthesized by adapting supercritical water as a reaction field forhydrothermal synthesis. However, there is no report for modification ofthe surface of the produced nanoparticles in this reaction field, orsynthesis of organically modified particles by a reaction with anorganic material.

A technique for performing an in-situ surface modificationsimultaneously with CVD in a supercritical fluid is also known, in whichalkanethiol or alcohol is made coexist in a reaction field forsynthesizing metal nanoparticles by CVD in the supercritical fluid,taking reference to the above-mentioned hot soap method or the like. Itis reported that the growth of particles can be inhibited to generateparticles of nanometer according to this technique. For the CVDtechnique, it is reported that the reduction reaction and surfacemodification by alkanethiol simultaneously occur, and the resultingproduct is metal Cu having an alkanethiol-coordinated structure. It isalso reported to produce nanoparticles by performing the synthesis inthe presence of alkanethiol similarly to the above by use of a reducingagent in supercritical water, thereby coordinating the thiol group withmetal nanoparticles to inhibit the growth of particles. In case of thealcohol, it is shown in a part of the result that not only orientationbut also linkage was caused to perform in-situ surface modification inthe reaction filed. However, this is caused not by the reactivecrystallization in supercritical “water”, but by only a techniquebelonging to reactive in-situ surface reforming method in an organicsolvent.

A surface treatment of glass or silica gel in water is well known, butthis method is based on CNBr activation or epoxy activation. Since eachof the CNBr method and the epoxy activation method is carried out in analkaline solution, particles of about nanometer (nm) are entirelydissolved. Therefore, these known reactions cannot be used for thesurface modification of oxide nanoparticles in water.

Conventional organic modification methods will be collectivelydescribed.

1) Synthesis of Organic-Inorganic Composite Material

Silane coupling is given as a general method for modifying a metal oxidesurface (Polymer Frontier 21 Series 15 “Inorganic/Polymer Nano InterfaceControl”, edited by Society of Polymer Science, pp. 3-23, NTS, 2003).There are researches for syntheses of organic/inorganic compositematerials [“Formation of Ordered Monolayer of Anionic Silica Particleson a Cationic Molecular Layer”, T. Yonezawa, S. Onoue, and T. Kunitake,Chem. Lett., No. 7, 689-690 (1998); Molecular Imprinting ofAzobenzeneCarboxylic Acid on a TiO2 Ultrathin Film by the Surface Sol-GelProcess”, S.-W. Lee, I. Ichinose, T. Kunitake, Langmuir, VoL 14,2857-2863 (1998); “Alternate Molecular Layers of Metal Oxides andHydroxyl Polymers Prepared by the Surface Sol-Gel Process”, I. Ichinose,T. Kawakami, T. Kunitake, Adv. Mater., Vol. 10, 635-539 (1998); and“Molecular Imprinting of Protected Amino Acids in Ultrathin Multilayersof TiO2 Gel”, S. W. Lee, I. Ichinose, T. Kunitake, Chem. Lett., No. 12.,1993-1994 (1998)]. Surface modifications of oxides in water are alsoknown. Techniques for surface-modifying glass or silica gel in waterinclude CNBr activation or epoxy activation, in which CNBr or epoxy isreacted with OH on the surface to give the functional group of the CN orepoxy, and an intended functional group is introduced through it.However, such a reaction requires setting of pH and addition of acatalyst, and involves generation of an acid as a product. Since theseactivations are carried out in an alkaline solution, all particles ofabout nm are dissolved, and it is therefore impossible to perform thesurface modification of oxide nanoparticles in water by use of theseknown reactions (Rolf Axen, Jerker Porath, Sverker Ernbvack, “ChemicaCoupling of Peptides and Proteins to Polysaccharides by Means ofCyanogen Halides”, Nature, Vol. 214, 1967, pp. 1302-1304). In everymethod described above, the organic modification depends on a reactionin an organic solvent. Particles of nano-size are easy to coagulatebecause of high surface energy. A solution method such as sol-gelprocess or hydrothermal process is effective, as shown in FIG. 1, insynthesizing particles of 10 nm or less. However, the particlessynthesized in a solvent are firmly coagulated, when taken out anddried, and it is extremely difficult to redisperse them in an organicsolvent. The solvent must be changed to the organic solvent stepwise.Particularly, the nanoparticles synthesized in water frequently havehydrophilic groups, and a pretreatment such as use of a surface activeagent is needed for dispersing them to an organic solvent. Accordingly,the technique for surface-modifying nanoparticles in situ whilesynthesizing them is important for synthesis of nano-particles of 50 nmor less.

2) Technique for Performing In-Situ Surface Modification ReversedMicelle Method

Water is suspended in an oil phase by use of a surface active agent toform a reversed micelle, and a reactive substrate is added thereto toreactively crystallize it. For example, CdS nanoparticles and NaNO₃ canbe generated by mixing an aqueous solution of Cd(NO)₂ with micelle ofNa₂S. The CdS nanoparticles can be stabilized by supplying a stabilizingagent such as alkanethiol. The surface active agent is in a stateadsorbed to the surface without a linkage by reaction (A) New Technologyfor Production, Evaluation, Application and Equipment of Nanoparticles”,pp. 16-19, 2002, published by CMC). Recently, a method usingsupercritical carbon dioxide as solvent has been also reported (Ye, X.R., Lin, Y. Wang, C., Wai, C. M., Adv. Materials, 2003, 15, 316; and Ye,X. R., Lin, Y. Wang, C., Wai, C. M., Chem. Comm., 2003, 642).

Hot Soap Method

The above-mentioned method is carried out at high temperature by use ofonly a surface active agent without oil phase. An aqueous solution ofmetal salt to be reacted is rapidly supplied with stirring andreactively crystallized, while the circumferential surface active agentis adsorbed thereto (A) “New Technology for Production, Evaluation,Application and Equipment of Nanoparticles”, pp. 19-21, 2002, publishedby CMC). Most of the cases reported up to now are based on adsorption ofalkanethiol, and no reactive modification has been practiced.

In-Situ Surface Modification in Supercritical Fluid by ReactiveCrystallization

A method for performing an organic modification simultaneously withthermal decomposition CVD (chemical vapor deposition) in a supercriticalfluid is also proposed. Particularly, an article for a surfacemodification performed in coexistence of alkanethiol in a supercriticalhydrothermal synthesis (Technoarch's Patent) field is disclosed. Whenthe coexistence of hexane thiol with an aqueous solution of Cu(NO₃)₂laid in a supercritical state results in synthesis of Cu particles byreduction and stabilization thereof by hexane thiol in situ. In thiscase, the thiol acts as a reducing agent to coordinate the hexane thiolwith the surface of the generated Cu nanoparticles. This is a well-knowncoordination with metal (Kirk J. Ziegler, R. Christopher Doty, Keith P.Johnston, and Brian A. Korgel, “Synthesis of OrganicMonolayer-Stabilized Copper Nanocrystals in Supercritical Water”, J. Am.Chem. Soc., 2001, 123, 7797-7803). Surface modification of SiO₂ withalcohol with synthesis thereof is also known (the same reference asabove Kirk J. Ziegler, R. Christopher Doty, Keith P. Jonston, and BrianA. Korgel, “Synthesis of Organic Monolayer Stabilized CopperNanocrystals in Supercritical Water”, J. Am. Chem. Soc., 2001, 123,7797-7803).

The present inventors have proposed a nanoparticle synthesis insupercritical water for synthesizing highly crystalline particles ofnano-size by adapting supercritical water as a reaction field forhydrothermal synthesis, but not referred to a process for modificationof the surface of the produced particles or synthesis of organicallymodified particles by a reaction with an organic matter. There arefrequently reported that high-temperature, high-pressure water forms ahomogenous phase also with an organic material and that water functionsas an acid or basic catalyst to progress an organic synthetic reactioneven in no catalyst in a high-temperature, high-pressure field. However,the process for reaction between an inorganic material and an organicmaterial has not been reported yet.

With respect to fine particles, particularly, nanoparticles, theusability of which is expected because of various useful properties andfunctions, a number of synthetic methods have been proposed anddeveloped, including the supercritical synthetic method. However, amethod for recovering the thus-synthesized fine particles ornanoparticles, and a method for dispersing and stabilizing the fineparticles as they are without coagulation after recovery are needed. Atthe time of use, they must be satisfactorily dispersed in a resin,plastic or solvent. Particularly, nanoparticles synthesized in water arenot easily recovered from water since they frequently have hydrophilicsurfaces. The nanoparticles or the like have the problem ofunfamiliarity with organic solvents, resins or the like.

In order to satisfy these needs, it might be necessary to modify thesurface of nanoparticles with organic materials according to therespective purposes. For example, modification with the same polymer asthe resin, or donation of the same functional group as the solvent isdesirable. If the nanoparticles can be surface-modified in water, theseparate recovery of the nanoparticles from water is facilitated.However, although it is desirable for the surface modification ofnanoparticles synthesized in water with an organic material that theorganic material forms a homogeneous phase with water, the modifyingagent usable therefor is limited to an amphipathic surface active agent,a lower alcohol soluble even to water, and the like. Further, even ifthe nanoparticles are recovered by any method, the recoverednanoparticles are extremely easy to coagulate, and it is difficult toredisperse the nanoparticles coagulated once even by use of adispersant. The surface modification of such nanoparticles is entirelydifficult.

It is well-known that water and an organic material form a homogenousphase in a high-temperature, high-pressure field and, for example,alcohol and sugar, carboxylic acid and alcohol, or carboxylic acid andamine non-catalytically cause a dehydration reaction inhigh-temperature, high-pressure water. However, it is not known that areaction is caused between hydroxyl group on the particle surface andthe organic material in this condition.

Thus, it is needed to develop the method for introducing a requireddesirable functional group to nanoparticles at the time of synthesisthereof in water. As a result of the earnest studies, the presentinventors found that synthesis of metal oxide particles in ahigh-temperature, high-pressure hydrothermal synthetic field in thecoexistence of an organic material results in surface-modified fineparticles having the organic material strongly bonded with the particlesurface by the occurrence of a homogenous phase reaction between theparticle surface and the organic material. It is also found that theresulting nanoparticles can be phase-separated from water with theremaining organic material, and easily recovered after cooling becausethey are organically modified. The present invention has beenaccomplished based on such knowledge.

SUMMARY OF THE INVENTION

The present invention provides the followings in typical aspects.

[1] Organically modified fine particles, including hydrocarbon stronglybonded with the surface of fine particles.

[2] The fine particles according to [1], wherein the hydrocarbon isstrongly bonded with the surface of metal oxide fine particles, and theorganically modified fine particles are organically modified metal oxidefine particles.

[3] The fine particles according to [1], wherein the average diameter ofthe fine particles is 100 nm or less.

[4] The fine particles according to [1], wherein the average diameter ofthe fine particles is 50 nm or less.

[5] The fine particles according to [1], wherein the average diameter ofthe fine particles is 20 nm or less.

[6] The fine particles according to [1], wherein the average diameter ofthe fine particles is 10 nm or less.

[7] The fine particles according to [1], wherein the average diameter ofthe fine particles is 5 nm or less.

[8] The fine particles according to any one of [1] to [7], wherein thehydrocarbon is a long-chain hydrocarbon having a chain having 1, 2, 3 ormore carbon atoms.

[9] The fine particles according to any one of [1] to [8], wherein thestrong bond is selected from the group consisting of ether bond, esterbond, bond through N atom, bond through S atom, metal-C— bond, metal-C═bond, and metal-(C═O)— bond.

[10] The fine particles according to any one of [1] to [9], wherein thecovering ratio of the particle surface for the organic modification isadjusted.

[11] The fine particles according to any one of [1] to [10], wherein thehydrocarbon is strongly bonded with the surface of the fine particleswith high-temperature, high-pressure water as a reaction field.

[12] The fine particles according to any one of [1] to [11], wherein thehydrocarbon is strongly bonded with the surface of the fine particleswith water of a supercritical or subcritical condition as a reactionfield.

[13] A process for producing organically modified metal oxide fineparticles, comprising strongly bonding an organic material with thesurface of metal oxide fine particles with high-temperature,high-pressure water as a reaction field, thereby synthesizingorganically modified metal oxide fine particles.

[14] The process according to [13], wherein water of pressure and/ortemperature conditions corresponding to or exceeding a critical point isadapted as the reaction field.

[15] The process according to [13] or [14], wherein the organicallymodified metal oxide fine particles are synthesized in a reaction fieldwhere water of conditions of temperature 250-500° C. and pressure 10-30MPa is present.

[16] The process according to any one of [13] to [15], wherein thehydrocarbon is a long-chain hydrocarbon having a chain having 1, 2, 3 ormore carbon atoms.

[17] The process according to any one of [13] to [16], wherein thestrong bond is selected from the group consisting of ether bond, esterbond, bond through N atom, bond through S atom, metal-C— bond, metal-C═bond, and metal-(C═O)— bond.

[18] The process according to any one of [13] to [17], wherein anorganic modifying agent is selected from the group consisting ofalcohol, aldehyde, carboxylic acid, amine, thiol, amide, ketone, oxime,phosgene, enamine, amino acid, peptide, and sugar.

[19] The process according to any one of [13] to [18], wherein a solventfor promoting the phase homogenization of the organic modifying agentwith water is used as a coexistent material.

[20] The process according to [19], wherein the solvent is selected fromthe group consisting of methanol, ethanol, propanol, i-propanol,butanol, i-butanol, t-butanol and ethylene glycol.

[21] The process according to any one of [13] to [18], wherein thereaction is carried out in the coexistence of an assistant for promotingthe reaction.

[22] The process according to [21], wherein the reaction promotingassistant is an acid.

[23] The process according to [22], wherein the acid is selected fromthe group consisting of nitric acid, sulfuric acid, hydrochloric acid,bromic acid, formic acid, acetic acid, propionic acid and toluenesulfonic acid.

[24] The process according to any one of [13] to [23], wherein thereaction ratio of the organic modification is controlled by controllinga factor selected from the group consisting of the temperature, the acidconcentration and the reaction time.

[25] A method for recovering or collecting fine particles, comprisingorganically modifying the surface of fine particles, thereby:

(1) precipitating and recovering metal oxide fine particles dispersed inan aqueous solution;

(2) transferring metal oxide fine particles dispersed in an aqueoussolution to an organic solvent followed by recovering; or

(3) collecting metal oxide fine particles in an oil phase-water phaseinterface.

[26] A process for producing fine particles, comprising producing metaloxide fine particles satisfactorily dispersed in an aqueous solution byorganic surface modification including hydrophilic groups.

[27] A process for producing organically modified metal oxide fineparticles, comprising producing metal oxide fine particles in thecoexistence of an organic modifying agent in a reaction field forsupercritical hydrothermal synthesis.

[28] The process according to [27], wherein the particle size of thegenerated particles is adjusted to a further small particle size.

[29] A process for producing organically modified metal oxide fineparticles, comprising subjecting a metal compound to a hydrothermalreaction with high-temperature, high-pressure water as a reaction fieldto form metal oxide fine particles, and strongly bonding an organicmatter to the surface of the formed metal oxide fine particles, therebysynthesizing organically modified metal oxide fine particles.

Fine particles with hydrophilic surface (particularly, nanoparticles)are surface-modified with the hydrophobic group of an organic mattersuch as hydrocarbon, whereby the particles which are difficult to berecovered from an aqueous medium can be easily and surely transferred toan organic medium and separated/recovered without impairing usefulcharacteristics of the fine particles (particularly, nanoparticles). Onthe other hand, hydrophobic fine particles (particularly, nanoparticles)can be transferred to and separated/recovered from an aqueous mediumside such as an aqueous solution by modifying the surface thereof with ahydrocarbon having hydrophilic group.

Since metal oxide fine particles (particularly, nanoparticles) presentin an aqueous medium hardly form a homogeneous reaction system with amodifying agent having organic group such as hydrophobic hydrocarbon,the fine particles (particularly, nanoparticles) could not beorganically modified without impairing the useful characteristics of theparticles. However, this can be made possible by applying themodification of the present invention. Further, since the degree ofmodification can be controlled, various unique characteristics can beimparted, respectively, by the modification.

Other objects, features and superiority of the present invention andaspects thereof will be obvious for those skilled in the art from thefollowing description. However, it should be understood that theaccompanying specification including the following description andconcrete examples describes preferred embodiments of the presentinvention and is disclosed only for illustration. It will be easilyunderstood by those skilled in the art from the following descriptionand the knowledge derived from other parts of the specification thatvarious changes and/or alternations (or modifications) can be madewithout departing from the intention and scope of the present invention.

All patent literatures and reference literatures cited herein aredescribed for illustration, and the content thereof should be includedherein as a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relation of density of water with pressure andtemperature on the left and the relation of dielectric constant of waterwith pressure and temperature on the right;

FIG. 2 shows the phase behavior of a water-gas binary system in thevicinity of a critical point of water (on the left), and the phasebehavior of a water-organic solvent system therein (on the right);

FIG. 3 shows a typical reactor used for organic modification accordingto the present invention;

FIG. 4 shows typical nanoparticles the use of which is desired withtypical production process and particle sizes thereof,

FIG. 5 shows a typical reaction system apparatus used for the organicmodification according to the present invention;

FIG. 6 schematically shows characteristics of the organic modificationmethod according to the present invention;

FIG. 7 schematically shows the mechanism of the modification reactionaccording to the present invention;

FIG. 8 shows metal oxide fine particles (TiO₂ nanoparticles)surface-modified with hexanal by the technique of the present invention(on the right), comparatively with non-modified particles (on the left);

FIG. 9 shows an IR spectrum of the modified particles resulted fromsurface modification of metal oxide fine particles (SiO₂ nanoparticles)with hexylamine by the technique of the present invention;

FIG. 10 shows metal oxide fine particles (TiO₂ nanoparticles)surface-modified with hexanoic acid by the technique of the presentinvention (on the right), comparatively with non-modified fine particles(on the left);

FIG. 11 shows an IR spectrum of the modified particles resulted fromsurface modification of metal oxide fine particles (TiO₂ nanoparticles)with hexanoic acid by the technique of the present invention;

FIG. 12 shows metal oxide fine particles (TiO₂ nanoparticles)surface-modified with asparaginic acid by the technique of the presentinvention (on the right), comparatively with non-modified particles (onthe left);

FIG. 13 comparatively shows metal oxide fine particles (SiO₂nanoparticles) surface-modified with decanoic acid (on the right) andwith decane amine (on the left) by the technique of the presentinvention, respectively;

FIG. 14 shows metal oxide fine particles hydrothermally synthesized bythe technique of the present invention, the surface of which isorganically modified in situ in the coexistence of hexanol (on theright), comparatively with non-modified particles (on the left);

FIG. 15 shows metal oxide fine particles (on the lower side) organicallymodified by the technique of the present invention and non-modifiedparticles (on the upper side) by TEM images;

FIG. 16 shows metal oxide fine particles hydrothermally synthesized bythe technique of the present invention, the surface of which isorganically modified in the coexistence of hexanol in situ (on theright), comparatively with non-modified particles (on the left);

FIG. 17 shows the result of in-situ organic modifications of metal oxidefine particles (CeO₂ nanoparticles) with varied treatment temperaturesby the technique of the present invention;

FIG. 18 shows the relation between a typical device configuration andparticle size obtained in each condition in the synthesis of fineparticles by executing a hydrothermal synthesis with high-temperature,high-pressure water such as subcritical or supercritical water as areaction field; and

FIG. 19 shows that metal oxide fine particles organically modified bythe technique of the present invention exhibits a property such as aunique dispersibility to medium by adjusting its affinity with asolvent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a technique for bonding an organic matterwith the surface of metal oxide fine particles with high-temperature,high-pressure water as a reaction field to synthesize organicallymodified metal oxide fine particles, particularly, organically modifiedmetal oxide nanoparticles, which are attracting attentions in recentyears because of their peculiar characteristics, the resultingorganically modified metal oxide fine particles, and usage and appliedtechnologies thereof. The present invention involves an organicmodification method paying attention to the point that water and anorganic material form a homogeneous phase in a reaction field showing acertain phase behavior. The features of this method are conceptually andschematically shown in FIG. 6.

As the reaction field of the modification reaction of the presentinvention, suitably, pressure and/or temperature conditionscorresponding to or exceeding the subcritical or critical point of waterare given. FIG. 1 shows the density of water-temperature/pressuredependency (on the left of FIG. 1) and the dielectric constant ofwater-pressure dependency (on the right of FIG. 1). As is apparenttherefrom, when the region of temperature/pressure corresponding to orexceeding the critical point of water is adapted as the reaction field,a unique reaction environment can be provided. FIG. 2 shows the phasebehavior of a water-gas binary system in the vicinity of the criticalpoint of water (on the left of FIG. 2) and the phase behavior of awaterorganic solvent system (on the right of FIG. 2), from which it isobvious that a characteristic homogenous phase forming region exists,and this is applicable to the modification reaction of the presentinvention.

At the time of using nanoparticles, by introducing a functional grouphaving high affinity with a solvent or resin to be used for to theparticles, the particles can be dispersed to the solvent or resin athigh concentration.

In the present invention, the particle size can be also controlled byperforming the in-situ surface modification in a reaction field forhydrothermal synthesis including a supercritical region.

The term “fine particles” referred to herein may indicate those with anaverage particle size of 1 μm (1,000 nm) or less and, preferably,nanoparticles. The nanoparticles may generally include those of anaverage particle size of 200 nm or less and, preferably, those of 200 nmor less. The nanoparticles can have an average particle size of 100 nmor less in a certain case, and an average particle size of 50 nm or lessin another case. The nanoparticles further can have an average particlesize of 20 nm or less in a suitable case, and an average particle sizeof 10 nm or less, or 5 nm or less in other cases. Although the particlesize of nanoparticles is preferably uniformed, those different inparticle size can be suitably mixed in a fixed ratio.

The particle size can be measured by a method known in the relevantfield, for example, by TEM, adsorption method, light scattering method,SAXS or the like. In the TEM, at the time of electron microscopicobservation, it must be carefully confirmed that particles within thefield of view are representative for all the particles when the particlesize distribution is wide. In the adsorption method, a BET surface areais evaluated by N₂ adsorption or the like.

Fine particles generated by means of hydrolysis reaction are generallycomposed of a hydroxide such as Fe(OH)₃, and the equilibrium is shiftedto FeO(OH) and Fe₂O₃ as the temperature is raised. The moleculararrangement state is shifted from a random amorphous state to a neatlyarranged crystal state as the temperature is raised. Highly crystallinenanoparticles which are organically modified can be obtained by usingthe technique of the present invention.

The high crystallinity can be confirmed by electron diffraction method,analysis of electron microgram, X-ray diffraction, thermogravimetry orthe like. In the electron diffraction, as a diffraction interferenceimage, dots are obtained in case of monocrystal, rings in polycrystal,and halos in amorphous. In the electron microgram, a crystal plane isclearly observed in case of monocrystal, and polycrystal has a shapesuch that crystals further appear from above particles. When primaryparticles of polycrystal are small, and many particles are coagulated toform a secondary particle, a spherical shape is observed. The amorphousnecessarily shows a spherical shape. In the X-ray diffraction, a sharppeak can be observed in case of monocrystal. The crystallite size can beevaluated from the width of ½ height of the X-ray peak by use ofSherre's expression. When the crystallite size obtained by thisevaluation is equal to the particle size evaluated from the electronmicroscopic image, monocrystal is evaluated. In the thermogravimetry,when heating is performed in a dry inactive gas by a thermobalance, areduction in weight by evaporation of adsorbed moisture is observed atabout 100° C., and a reduction in weight by dehydration from theparticles is observed up to about 250° C. If an organic material iscontained, a further large reduction in weight is observed at 250-400°C. In case of the particles obtained by the technique of the presentinvention, even if the temperature is raised to 400° C., the reductionin weight by dehydration from the crystals is 10% or less at a maximum,greatly different from the case of metal oxide fine particlessynthesized at low temperature. Accordingly, the fine particles oforganically modified metal oxide fine particles obtained according tothe present invention have high crystallinity as features; for example,they have sharp peaks in X-ray diffraction, dote or rings are observedin electron diffraction, dehydration of crystal water is 10% or less perdry particle in thermogravimetry, and/or the primary particle has acrystal plane in electron microgram.

When a separating or dispersing operation of fine particles is performedin relative to particle size by opposing the surface energy with anexternal energy such as gravity or electric field or by means ofcentrifugal force, gravity settling, electrophoresis, or the like,particles with a particle size of several 100 nm or less can bedispersed only when a large external field force is given thereto. Witha particle size of 50 nm or less, the influence of the surface energy isfurther increased, and the dispersion is extremely difficult only withthe external field energy, unless the surface property, the physicalproperty of the solvent, or the like is controlled. The technique of thepresent invention can solve this problem.

Particularly, when the particle size is 10 nm or less, the overlappingin a quantum state is eliminated, and the electron state on the surfaceseriously affects the bulk physical properties. Therefore, physicalproperties completely different from those of bulk particles can beobtained, or a quantum size effect (Kubo's effect) is exhibited.Although the particles of a size of about 10 nm or less can be regardedparticularly as completely different materials, such fine nanoparticlescan be suitably organically modified according to the technique of thepresent invention.

Typical fine particles in the present invention include thoseessentially composed of a metal oxide, and these will be hereinafterreferred to as “metal oxide fine particles”.

As the “metal” in a metal oxide contained in the metal oxide fineparticles, typically, any metal capable of producing nanoparticles canbe selected and used, without particular limitation, from metals knownby those skilled in the art. Examples of typical metals include, withthe line connecting boron (B) of the group IIIB, silicon (Si) of thegroup IVB, arsenic (As) of the group VB, and tellurium (Te) of the groupVIB in the long-period periodic table as a border, elements located onthis line and elements situated on the left side or the lower side ofthe border in the long-period periodic table, including Fe, Co, Ni, Ru,Rh, Pd, Os, Ir, Pt, etc. as elements of the VIII group; Cu, Ag, Au, etc.as elements of the group IB; Zn, Cd, Hg, etc. as elements of the groupIIB; B, Al, Ga, In, Tl, etc. as elements of the group IIIB; Si, Ge, Sn,Pb, etc. as elements of the group IVB; As, Sb, Bi, etc. as elements ofthe group VB; Te, Po, etc. as elements of the group VIB; and elements ofthe groups IA-VIIA. Examples of the metal oxide include oxides of Fe,Co, Ni, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, TI, Si, Ge, Sn, Pb, Ti, Zr,Mn, Eu, Y, Nb, Ce, Ba, etc., and concrete examples thereof include SiO₂,TiO₂, ZnO₂, SnO₂, Al₂O₃, MnO₂, NiO, Eu₂O₃, Y₂O₃, Nb₂O₃, InO, ZnO, Fe₂O₃,Fe₃O₄, Co₃O₄, ZrO₂, CeO₂, BaO.6Fe₂O₃, Al₆(Y+Tb)₃O₂, BaTiO₃, LiCoO₂,LiMn₂O₄, K₂.6TiO₂, AlOOH, and the like.

In the organic modification of the surface of fine particles,particularly, nanoparticles, any device capable of attaining ahigh-temperature, high-pressure condition can be selected and used,without particular limitation, from devices well-known by those skilledin the art in the relevant field. For example, both a batch device and adistribution type device are applicable. A typical reactor is shown inFIG. 3 as an example, which may a system as shown in FIG. 5. A properreaction device can be constituted as occasion demands.

As the organic modifying agent, those capable of strongly bondinghydrocarbon with the surface of fine particles can be selected, withoutparticular limitation, from organic materials well-known in the fieldswhere the application of nanoparticles is expected, including the fieldsof organic chemistry, inorganic material, and polymer chemistry. As theorganic modifying agent, for example, those permitting formation of astrong bond such as ether bond, ester bond, bond through N atom, bondthrough S atom, metal-C— bond, metal-C═ bond, metal-(C═O)-bond or thelike are given. As the hydrocarbon, those having 1 or 2 carbon atoms canbe used without particularly limiting the carbon number. From the pointof effectively using the features of the present invention, a long-chainhydrocarbon having a chain having 3 or more carbon atoms is preferablyused, and examples thereof include straight-chain, branched-chain orcyclic hydrocarbons having 3-20 carbon atoms. The hydrocarbons may besubstituted or non-substituted. The substituent may be selected fromfunctional groups well-known in the fields of organic chemistry,inorganic material, polymer chemistry and the like, and one or moresubstituents can exist in the hydrocarbon, wherein the substituents maybe the same or different.

Examples of the organic modifying agent include alcohols, aldehydes,ketones, carboxylic acids, esters, amines, thiols, amides, oximes,phosgenes, enamines, amino acids, peptides, sugars and the like.

Typical modifying agents include pentanol, pentanal, pentanoic acid,pentane amide, pentathiol, hexanol, hexanal, hexanoic acid, hexaneamide, hexane thiol, heptanol, heptanal, heptanoic acid, heptane amide,heptane thiol, octanol, octanal, octanoic acid, octane amide, octanethiol, decanol, decanal, decanic acid, decane amide, decane thiol, andthe like.

Examples of the hydrocarbon group include a straight-chain orbranched-chain alkyl group which may be substituted, a cyclic alkylgroup which may be substituted, an aryl group which may be substituted,an aralkyl group which may be substituted, a saturated or unsaturatedheterocyclic group which may be substituted, and the like. Examples ofthe substituent include carboxyl group, cyano group, nitro group,halogen, ester group, amide group, ketone group, formyl group, ethergroup, hydroxyl group, amino group, sulfonyl group, —O—, —NH—, —S— andthe like.

Reaction Mechanism

A hydroxyl group is generally present on the surface of a metal oxide inwater. This is resulted from the following equilibrium in reaction.

MO+H₂O=M(OH)  (1)

This reaction is generally endothermic, and the equilibrium is shiftedto the left at a high temperature side. The reaction by the surfacemodifying agent used is as follows, and it is caused by dehydrationreaction.

The left-pointing reaction (reverse reaction) is a reaction well-knownas hydrolysis of alkoxide or the like, which is easily caused byaddition of water even at about room temperature. This reverse reactionis generally inhibited at high temperature side because it is anendothermic reaction, and the right-pointing reaction becomes moreadvantageous. This is the same as the temperature dependency of thedehydration reaction of metal hydroxide of equation (1).

The product in water is stabilized more advantageously as the polarityof the solvent is lower, since the polarity of the product is low in theright-pointing reaction (dehydration), compared with in the reactionoriginal system. The higher the temperature is, the lower the dielectricconstant of water is. The dielectric constant is reduced to 15 or lessat 350° C. or less and suddenly reduced to about 1-10, particularly, inthe vicinity of the critical point. Therefore, the dehydration reactionis accelerated beyond a general temperature effect.

M(OH)+ROH=M(OR)+H₂O=M.R+2H₂O

M(OH)+RCOOH=M(OCOR)+H₂O=MR+H₂O+CO₂

M(OH)+RCHO=M(OH)CR+H₂O=MC═R+2H₂O,MCR+2H₂O,

MR+H₂+CO₂

M(OH)+RSH=MSR+H₂O(reduction)

(these equations are referred to as (2))

Although it is known that the attack on hydroxyl group by amineprogresses in the coexistence of a strong acid or through a substitutionby Cl at room temperature, its replacement with OH occurs inhigh-temperature, high-pressure water. It is confirmed, with respect toorganic materials, that amination of hexanol progresses with carboxylicacid as a catalyst between hexane amide and hexanol, and it can bepresumed that a similar reaction is proceeding. A part of the reactionmechanism of this technique is schematically shown in FIG. 7 as anexample.

In case of thiol, the probability of reduction in the reaction field isreported and it can be presumed that the thiol was partially reduced onthe metal oxide surface, causing a thiol additive reaction thereby.

Setting Method of Conditions 1) Equilibrium in Reaction

The reaction condition causing the organic modification can besummarized as followed although it is varied depending on the kind ofmetals and the modifying agent.

When the equilibrium of equation (1) is on the right and the equilibriumof equation (2) is on the right, the reaction progresses. Since therespective equilibriums are varied depending on the kind of metals andmodifying agent, the optimum reaction condition therefor is also varied.When the temperature is raised, the equilibrium of equation (2) isshifted to the right and suddenly shifted to the progress side,particularly, at 350° C. or higher, while the equilibrium of equation(1) is shifted to the left. For the reaction conditions, DB of equations(1) and (2) are referred to.

Since the functional group on the surface of the metal oxide can be madeto OH by coexistence of a base or acid, the dehydration reaction withthe modifying agent can be progressed in this condition. In that case,since the dehydration reaction is apt to occur in the presence of theacid, the reaction can be progressed by slight coexistence of the acidat high temperature.

2) Phase Equilibrium

Since alcohols, aldehydes, carboxylic acids and amines which arerelatively short-chain hydrocarbons are soluble to water, for example,surface modification of the metal oxide with methanol is possible.However, in case of long-chain hydrocarbons, since phase separation fromwater phase is caused, the metal oxide actually located in water phasemay not react with the organic modifying agent even if the equilibriumin reaction gets closer to the progress side. Namely, introduction oflipophilic group is relatively easy, but the phase behavior must betaken into consideration when a long-chain hydrocarbon having three ormore carbon atoms is intended.

The phase behavior of hydrocarbon and water is already reported, andthis can be referred to. In general, since they form a homogeneous phasein an optional ratio with a vapor-liquid critical locus or more, suchtemperature/pressure conditions are set, whereby a satisfactory reactioncondition can be set.

When a further lower optimum reaction temperature is desired, a thirdcomponent can be made to coexist to form a homogeneous phase of waterand the organic matter. For example, it is known that the coexistentregion of hexanol and water can be formed at a further low temperatureby the coexistence of ethanol or ethylene glycol which forms ahomogeneous phase with water even at low temperature. This can beapplied to the reaction of a metal oxide and an organic material. Inthis case, it is important to select the third component so as not tocause a surface modification reaction by the third component.

The long-chain organic modification in water can be performed only bythe above-mentioned technique.

In-Situ Surface Modification in Hydrothermal Synthesis

As described above, the generation of hydroxyl group on the metal oxidesurface of equation (1) and the temperature dependency of organicmodification reaction of equation (2) are reversed. Therefore, when thereaction of equation (1) is on the left or on the dehydration side, inorder to cause a surface modification reaction, the setting of thereaction condition such as coexistence of an acid becomes extremelyimportant, but might be difficult.

The in-situ surface modification in hydrothermal synthesis enables this.

The hydrothermal synthesis progresses by the following reaction route.

Al(NO₃)₃+3H₂O═Al(OH)₃+3HNO₃

nAl(OH)₃ =nAlO(OH)+nH₂O

nAlO(OH)=n/2Al₂O₃ +n/2H₂O

In use of other metal spices and sulfates, hydrochlorides or the like,the synthesis progresses also by such a route. When the hydrothermalsynthesis is carried out, for example, by use of a device as shown inFIG. 18 with high-temperature, high-pressure water as a reaction field,particles of a further minute particle size can be obtained as shown inFIG. 18. Therefore, it will be obvious that further fine organicallymodified particles can be obtained according to the in-situ surfacemodification technique. It will be also obvious that the size ofparticles can be controlled by adjusting the temperature or pressure.

As shown herein, even if the hydroxyl group is finally desorbed from thesurface by the dehydration reaction, many hydroxyl groups are generatedin a product or on the surface thereof as a reaction precursor. If theorganic modifying agent is coexistent in this reaction field, thereaction can be carried out in a condition where the hydroxyl groups arepresent. Since the acid also as a catalyst for proceeding thedehydration reaction is coexistent in the reaction field, themodification reaction is accelerated. Accordingly, the surfacemodification which could not be performed to oxides can be carried out.

According to the technique of the present invention, the surface of fineparticles can be organically modified without being based on that theequilibration to an oxide by attainment of a high-temperature field,such that a precursor is once synthesized and then subjected tohydrolysis or the like to synthesize a metal oxide or metal hydroxide,or without using a surface radical polymerizing substrate, for example,an oxidizing material sensitive to temperature or light. Accordingly,metal particles or particles with different oxidation-reduction statescan be organically surface-modified.

In the present invention, synthesis of an inorganic-organic compositematerial is attempted by use of a phase state such that water and anorganic material forms a homogeneous phase, in which the surface ofhighly crystalline metal or metal oxide nanoparticles of a size ofseveral nm to 50 nm or less is modified with an organic molecule whilesynthesizing them. By using the high-temperature, high-pressure waterhydrothermal synthetic method therein, the conventional problems of 1)organically modifying the surface of highly crystalline nanoparticleswhile synthesizing it and 2) forming a polymer film of single layer canbe solved. Further, the conventional industrial problems of 1) recoveryof nanoparticles from a reaction solvent; 2) stable dispersion andretention thereof over a long period at high concentration in thesolvent; 3) homogenous dispersion thereof with a polymer in highconcentration; and 4) two-dimensional arrangement of nanoparticles canbe solved thereby.

Various nanoparticle synthetic methods such as CVD, PVD, atomizationthermal decomposition, sol-gel process, reversed micelle method, hotsoap method, and supercritical hydrothermal synthesis have beendeveloped. However, because nanoparticles are easily coagulated withextremely high surface energy, natural physical properties thereofcannot be often exhibited. A method for recovering the nanoparticles isneeded. Further, the nanoparticles must be dispersed and stabilizedafter recovery. The nanoparticles must be satisfactorily dispersed to aresin, plastic or solvent at the time of use. To satisfy these needs, itis necessary to modify the surface of the nanoparticles with organicmaterials according to the respective purposes. It is desirable tomodify the same polymer as the resin and the same functional group asthe solvent. These can be solved by the present invention.

Some techniques for surface-modifying the nanoparticles are proposed.However, with a conventional weak linkage such as coordination of thiolwith a metal surface or adsorption of a surface active agent to a metaloxide, semiconductor characteristic, fluorescent characteristic, lightemitting characteristic, dielectric characteristic and the like, whichare developed by making particles to a nano-size, might be lost. If ametal or metal oxide can be covalent-bonded with an organic molecule,nonconventional characteristics of nanoparticles can be derived. InBaTiO₃, for example, although a dielectric loss appears in an adsorptionlayer, it can be significantly reduced in a covalent-bond molecule.

The technique for performing the organic modification by forming thecovalent bond includes use of a silane coupling agent. In this case,formation of a Si atom layer on the nanoparticle surface might cause aloss of semiconductor characteristic, fluorescent characteristic, lightemitting characteristic, dielectric characteristic and the like of thenanoparticles similarly to the above. Introduction of a functional groupby use of a chloro-compound is also included. This might causedissolution of nanoparticles in the modification reaction condition (ina high pH or a low pH). These problems can be solved by the presentinvention. According to the present invention, a high-temperature,high-pressure hydrothermal synthetic method can be adapted, and highlycrystal nanoparticles can be organically modified with synthesisthereof. When an organic material is made coexist in a high-temperature,high-pressure hydrothermal synthetic field, a strong surfacemodification having the organic material bonded with the surface ofmetal oxide particles is formed by the homogeneous phase reaction of theorganic material with the particle surface, while synthesizing theparticles. Even particles of a particle size of 50 nm or less can besufficiently provided while keeping extremely high crystallinity. Thehigh-temperature, high-pressure water forms a homogenous phase even withthe organic material. An organic-inorganic combination is formed on thegenerated particle surface. Since other reactions such as polymerizationreaction are never caused, modification of only one layer can beperformed. The surface modification inhibits the crystal growth toenable synthesis of nanoparticles. At the time of synthesis, an in-situhigh-temperature thermal treatment effect can be obtained to enhance thecrystallinity.

In the present invention, use of an organic/inorganic composite body asa precursor is not requested as a means for synthesizing nanoparticles,and the applicable range thereof is remarkably excellent.

Consequently, the following effects can be expected.

1) Recovery of Nanoparticles from Water Phase.

The nanoparticles synthesized in supercritical water are generallysuspended in water. However, they can be transferred to oil phase by thesurface modification of the present invention, and perfectly separatedfrom water.

The recovery of the nanoparticles was extremely difficult. Althoughaddition of a coagulating agent or use of a surface active agent oradsorbent is empirically adapted, a technique for further recovering thenanoparticles therefrom is needed, and a new dispersing technique isalso requested to disperse them. According to the technique of thepresent invention, the particles can be recovered as they are withoutrequiring such an operation.

2) Satisfactory Dispersion of Nanoparticles in an Organic Solvent,Super-High Concentration Dispersion Possible in Principle

Hydrophilic titania particles were suspended in water, but transferredfrom water to chloroform phase by the surface modification of thepresent invention.

The surface modification can be performed while performing crystalprecipitation without surface modifying operation, a surface reformingoperation with a surface active agent or the like as in the past.Although the conventional methods had a limitation for introduction of amodifying group, an optional modifying group can be introduced.Accordingly, a solvent most suitable to a resin or solvent can beselected. The same molecule as the resin or solvent is used, wherebyultimately high-concentration dispersion and even dispersion withoutusing the solvent or resin can be performed.

3) Interface Arrangement by Surface Modification with ControlledCovering Ratio

It was observed that, when the covering ratio is reduced by controllingthe reaction, particles are arranged in the interface of water and oil.Accordingly, in addition to the recovery of particles, a nanoparticlearrangement can be performed by using the technique of the presentinvention.

4) Continuous Control of Dispersibility

The nanoparticles dispersed in water can be easily precipitated by useof a proper solvent system such as a solution of water:ethanol=50:50 bysurface-modifying them according to the technique of the presentinvention. The concentration at which the precipitation starts can becontinuously changed by controlling the degree of surface modification.Concretely, for example, a phenomenon as shown in FIG. 19 can beattained.

5) Presentation of Selective Recognition Ability

Nanoparticles modified with a functional group forming no chemical bondtherewith or nanoparticles modified with a functional group forming achemical bond therewith can be produced. The mutually bonding abilitycan be given by such a surface modification, and a high-order structureof nanoparticles can be formed by use of the technique of the presentinvention.

The nanoparticles are applied to various uses; for example, SiO₂ for apigment, a catalyst carrier, a high-temperature material, a honeycomb,an anticorrosive material, etc.; Fe₂O₃ for a pigment, a magneticmaterial, etc.; CeO₂ for an abrasive material, a catalyst carrier, anion conductor, a solid electrolyte, etc.; TiO₂ for a photocatalyst, acosmetic, etc.; Y₂O₃ for a pigment, a catalyst carrier, etc.; InO for atransparent conductor, etc.; ZnO for a phosphor material, a conductivematerial, a pigment, a electronic material, etc.; SiO₂ for a catalystcarrier, a zeolite, a filler, a bead, etc.; SnO₂ for a conductivematerial, a conductor, a sensor, a honeycomb, etc.; Nb₂O₃ for a magneticmaterial, etc.; Cu, Ag or Al for an electrode, a catalyst material,etc.; Ni for an electrode, a magnetic material, a catalyst material,etc.; Co or Fe for a magnetic material, a catalyst material, etc.; Ag/Cufor an electrode, a catalyst material, etc.; and B₄C, AlN, TiB₂ and thelike for a high-temperature material, a high-strength material, etc.

The nanoparticles or a thin film having a specified arrangement of thenanoparticles are recognized to show unique excellent characteristics,respectively. For example, it is known that nanoparticles arranged in asingle layer, or magnetic nanoparticles show excellent functions as anear-field storage medium, in which the nanoparticles can be compactlyfilled. They effectively exhibit excellent characteristics inapplication to a magnetic tape or the like. Since a quantum size effectcan be obtained in nanoparticles arranged in a dispersion systempattern, for example, a nanophosphor, a product such as quantum effectphosphor, quantum effect light emitter, or LSI high-density mountingbase can be provided. A multilayer simultaneous arrangement ofnanoparticles such as titania shows excellent functions such as lowlight scattering and photocatalyst effect, and is made into a wetphotoelectric conversion element, a high-function photocatalyst coatingor the like. A particle-dispersed film shows excellent functions such asa reinforcing effect or an inflammable effect, and is made into asemiconductor sealant or the like. Typical nanoparticles and fineparticles and the preparation methods and particle sizes thereof will beunderstood in reference to FIG. 4.

Fine particles (including nanoparticles) organically surface-modifiedaccording to the present invention function as particles suitable tousers' needs. For example, the particles are useful as ahigh-concentration barium titanate-dispersed resin for semiconductorpackaging, nanoparticle-dispersed ink for ink jet, a battery material, acatalyst material, a lubricant or the like, and such a material can beprepared as follows.

An electronic part such as a semiconductor is needed to be packaged witha high-dielectric constant resin in order to eliminate electricdisturbance out of the package. A barium titanate particle-dispersedthermosetting resin is used therefor. A high-concentration bariumtitanate-dispersed resin for packaging a semiconductor requires highconcentration dispersion of barium titanate particles. Although thebarium titanate can be dispersed in a resin using a surface activeagent, it has the problem of causing a dielectric loss in the interface.By using the technique for producing organic modified fine particles ofthe present invention, surface-modified particles with strong linkagecan be synthesized, and by introducing the same monomer as the resin, amaterial in which the resin is integrated with the organic material canbe ultimately synthesized.

The nanoparticles are used for ink for high-tech equipment, for example,nanoparticle-dispersed ink for ink jet because of excellent physicalproperties such as hue, satisfactory coloring and durability. An ink jetprinter by the ink dispersed with nanoparticles is expected to be usedfor formation of wiring and circuit diagrams by ink jet. However, tothat end, it is necessary to synthesize nanoparticles suitable theretoand disperse them to a solvent in a high concentration. According to thetechnique for producing organically modified fine particles of thepresent invention, particles having the same polymer as an ink solventcan be synthesized.

A battery material, for example, an electrode material such as an Li ionbattery or a capacitor material, is mixed with a carbonaceous materialand made to a material for product. The battery material is needed to besufficiently dispersed to carbon and a solvent. In general, a treatmentusing a dispersant is needed. According to the technique for producingorganically modified fine particles of the present invention, a materialhomogenously dispersible with the solvent can be synthesized withoutusing the dispersant.

A carrier metal catalyst is activated by a charge transfer caused by theinteraction of the orbital function of the metal with an oxide catalyst.By using the technique for producing organically modified fine particlesof the present invention, capable of mixing dissimilar materials in ananometer order, a catalyst having activating points where the metalmakes contact with the oxide in a high density can be prepared toproduce an excellent catalyst material.

A lubricant, which is used to reduce the friction acting between solidbodies, can be expected to work as a nano-bearing by including thenanoparticles therein. Concretely, shearing force is converted to therotating motion energy of the bearing, whereby the transmission to theother side of the shearing force is prevented. Conventionally, anorganic polymer has been used as the lubricant, and oxide nanoparticleshaving a strong structure can be dispersed thereto by the technique forproducing organically modified fine particles of the present invention.

The present invention will be further concretely described with workingexamples. The examples are provided simply to be illustrative of thepresent invention and informative for concrete embodiments thereof.These examples describe specified concrete embodiments of the presentinvention, but never limit the scope of the invention disclosed in thepresent application or indicate a limitation thereof. It should beunderstood that various embodiments can be made based on the ideaherein.

All the examples were executed or can be executed by use of standardtechniques, except those described in detail, and they are well-knownand regular for those skilled in the art.

Example 1 (Organic Modification of Metal Oxide Fine Particles inHigh-Temperature, High-Pressure Water)

An experiment was carried out using a 5 cc-tubular autoclave (tube bombreactor). TiO₂ nanoparticles 0.1 g was charged in a reactor tube withpure water 2.6 cc and hexanal 0.1 cc. The reactor tube was put in aheating furnace preliminarily set to 400° C., and heated. The pressureis 390 bar on the assumption of pure water. It took 1.5 min to raise thetemperature. The reaction was carried out for 10 min. The reaction wasstopped by putting the reactor tube to cold water. The product wasrecovered by repeating washing with water and washing with chloroformtwice. The recovered product is shown on the right of FIG. 8. In case ofusing no hexanal, the recovered product is in a state suspended in wateras shown in the left of FIG. 8. This is caused by generation ofhydrophilic groups. Such a remarkable difference cannot be observed onlyby mixing a modifying agent without reaction, showing that this is notresulted from physical adsorption of a modifying group. According to theIR spectral measurement of the resulting particles, the hydroxyl groupson the surface are reduced, linkages of Ti—O—R, Ti—(C═O)—R, and Ti—Rwere observed. The formation of covalent bond by the reaction could beconfirmed.

Accordingly, surface modification of a metal oxide can be performed byusing high-temperature, high-pressure water as a reaction solvent.

Example 2 (Organic Modification of Metal Oxide Fine Particles inHigh-Temperature, High-Pressure Water)

An experiment was carried out using a 5-cc tubular autoclave (tube bombreactor) similarly to Example 1. SiO₂ nanoparticles 0.1 g was charged ina reactor tube with pure water 2.5 cc and hexylamine 0.1 cc. The reactortube was put in a heating furnace preliminarily set to 400° C., andheated. The pressure is 390 bar on the assumption of pure water. It took1.5 min to raise the temperature. The reaction was carried out for 10min. The reaction was stopped by putting the reactor tube to cold water.The product was recovered by repeating washing with water and washingwith chloroform twice. In case of using no hexylamine, the recoveredproduct is in a state suspended in water similarly to Example 1. This iscaused by generation of hydrophilic groups. In contrast, when themodification was performed, the particles were collected to theinterface between chloroform and water. It was found therefrom that themodification is too imperfect to provide a sufficient wetting angle towater and chloroform, the particles are not transferred to thechloroform phase but collected to the interface. A controlled organicmodification in high-temperature, high-pressure water shows theprobability of collection of a metal oxide to the interface. In thiscase, also, such a remarkable difference cannot be observed only bymixing a modifying agent without reaction, showing that this is notresulted from physical adsorption of a modifying group. According to theIR spectral measurement of the resulting particles, peaks of CH₂ and CH₂were observed on the surface (FIG. 9). Accordingly, the formation ofcovalent bond by the reaction could be confirmed.

Example 31 (Amino Acid Modification of Metal Oxide Fine Particles inHigh-Temperature, High-Pressure Water)

An experimental reaction was carried out using a 5 cc-tubular autoclave(tube bomb reactor).

SiO₂ nanoparticles 0.1 g was charged in a reactor tube with pure water2.5 cc and cysteine 100 mg. The reactor tube was put in a heatingfurnace preliminarily set to 400° C., and heated. The pressure is 390bar on the assumption of pure water. It took 1.5 min to raise thetemperature. The reaction was carried out for 10 min. The reaction wasstopped by putting the reactor tube to cold water. The recoveredparticles are perfectly dispersed in water more satisfactorily than inthe suspended state before reaction. This shows that coagulation of SiO₂is prevented by donation of hydrophilic groups to enhance thedispersibility.

Similarly to Examples 1 and 2, such a remarkable difference cannot beobserved only by mixing a modifying agent without reaction, showing thatthis is not resulted from physical adsorption of a modifying group.According to the IR spectral measurement of the resulting particles,COOH and NH₂ groups are reduced, while linkages of Si—N—R and SIO—(CO)Rare observed on the surface. Accordingly, the formation of covalent bondby the reaction could be confirmed.

Example 4 (Organic Modification of Metal Oxide Fine Particles inHigh-Temperature, High-Pressure Water in Coexistence of Acid)

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor).

Al₂O₃ nanoparticles 0.1 g was charged in a reactor tube with 0.1Maqueous solution of H₂SO₄ 2.5 cc and hexanal 0.1 cc. The reactor tubewas put in a heating furnace preliminarily set to 400° C., and heated.The pressure is 390 bar on the assumption of pure water. It took 1.5 minto raise the temperature. The reaction was carried out for 10 min. Thereaction was stopped by putting the reactor tube to cold water. Theproduct was recovered by repeating washing with water and washing withchloroform twice. An experiment for recovering the product not withchloroform but with hexanol was also carried out in the same manner.

In case of using pure water without addition of the acid, the recoveredproduct is in a state precipitated in the bottom of the chloroform phase(the lower phase). This is the same as the result of the experimentwithout surface treatment. In contrast, when the surface modification isperformed in the coexistence of the acid, the product is laid in a statepartially suspended in the chloroform phase. When recovered withhexanol, the product is partially suspended in the hexanol and partiallycollected to the interface between hexanol (the upper phase) and water.This shows that the surface treatment reaction progresses by thecoexistence of the acid. Even in such a reaction system where theorganic modification is difficult to progress, the reaction can beprogressed by the coexistence of the acid. The same experiment wascarried out for ZnO which was difficult to modify, and it was confirmedthat the coexistence of the acid enables the modification thereof.

Example 5 (Long-Chain Organic Modification of Metal Oxide Fine Particlesin High-Temperature, High-Pressure Water)

An experimental reaction was carried out using a 5 cc-tubular autoclave(tube bomb reactor).

SiO₂ nanoparticles 0.1 g was charged in a reactor tube with pure water1.5 cc and dodecanal 1 cc. The reactor tube was put in a heating furnacepreliminarily set to 400° C., and heated. The pressure is 390 bar on theassumption of pure water. It took 1.5 min to raise the temperature. Thereaction was carried out for 10 min. The reaction was stopped by puttingthe reactor tube to cold water. The product was recovered by repeatingwashing with water and washing with chloroform twice. The sameexperiment was carried out by use of hexanal.

In case of using no decanal, the recovered product was in a statesuspended in water. In contrast, when the modification was performed,the particles were collected to the interface between chloroform andwater at 400° C., showing that the modification was attained. In case ofusing hexanal, the reaction was satisfactorily progressed at 300° C. and400° C., and a slight progress of the reaction was confirmed further at200° C. However, in case of using dodecanal, satisfactory surfacemodification could be performed at 400° C., but the reaction was notprogressed at all at 200° C. Even at 300° C., the degree of progress ofthe reaction was low, compared with the case of hexanal.

Sufficient examples for the phase behavior of alkane-water phase werereported, and formation of a heterogeneous phase was probably caused atlow temperature, drawing up the phase behavior of the dodecane-watersystem.

Example 61 (Organic Modification of Metal Oxide Fine Particles inHigh-Temperature, High-Pressure Water)

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). TiO₂ nanoparticles 0.1 g was charged in a reactortube with pure water 2.5 cc and hexanoic acid 0.1 cc. The reactor tubewas put in a heating furnace preliminarily set to 400° C., and heated.The pressure is 390 bar on the assumption of pure water. It took 1.5 minto raise the temperature. The reaction was carried out for 10 min. Thereaction was stopped by putting the reactor tube to cold water. Theproduct was recovered by repeating washing with water and washing withchloroform twice. The recovered product is shown in FIG. 10.

In case of using no hexanoic acid or performing no surface modification,the recovered product is in a state suspended in water (the upper phase)as shown in the left of FIG. 10. However, the nanoparticlessurface-modified with hexanoic acid were transferred to the chloroformphase (the lower phase). This suggests that hydrophilic groups (OH) aregenerated on the surface of TiO₂ nanoparticles when the surfacemodification is not performed. In contrast, hydrophobic groups areintroduced to the particle surface as a result of surface modificationwith hexanoic acid. Such a remarkable difference cannot be observed onlyby mixing a modifying agent without reaction, showing that this is notcaused physical adsorption of a modifying group. According to the IRspectral measurement of the resulting particles, as shown in FIG. 11,peaks of CH₃ and CH₂ couplings were observed. According to this, theformation of covalent bond by the reaction could be confirmed.

By using high-temperature, high-pressure water as a reaction solvent,surface modification of a metal oxide can be performed. The same resultis also obtained in the use of hexanamide.

Example 7

(Organic Modification of Meal Oxide Fine Particles in High-Temperature,High-Pressure Water with Amino Acid)

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). TiO₂ nanoparticles 0.1 g was charged in a reactortube with pure water 2.5 cc and asparaginic acid 100 mg. The reactortube was put in a heating furnace preliminarily set to 400° C., andheated. The pressure is 390 bar on the assumption of pure water. It took1.5 min to raise the temperature. The reaction was carried out for 10min. The reaction was stopped by putting the reactor tube to cold water.The recovered particles were perfectly dispersed in water moresatisfactorily (the right of FIG. 12) than in the state suspended inwater before the reaction (the light of FIG. 12). This shows thatcoagulation of TiO₂ can be prevented by donation of hydrophilic groupsto enhance the dispersibility.

Similarly to Examples 2 and 6, such a remarkable difference cannot beobserved only by mixing a modifying agent without reaction, showing thatthis is not caused by physical adsorption of a modifying group.According to the IR spectral measurement of the resulting particles,COOH and NH₂ groups were reduced, while linkages of Ti—N—R, TiO—(CO)Rand Ti—R were observed on the surface. According to this, the formationof covalent bond by the reaction could be confirmed.

Example 8

(Organic Modification of Metal Oxide Fine Particles in High-Temperature,High-Pressure Water with Long-Chain Hydrocarbon)

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). SiO₂ nanoparticles 0.1 g was charged in a reactortube with pure water 1.5 cc and decanoic acid 1 cc. The reactor tube wasput in a heating furnace preliminarily set to 400° C., and heated. Thepressure is 390 bar on the assumption of pure water. It took 1.5 min toraise the temperature. The reaction was carried out for 10 min. Thereaction was stopped by putting the reactor tube to cold water. Theproduct was recovered by repeating washing with water and washing withhexadecane twice. The recovered product is shown in the right of FIG.13. In case of using no decanoic acid, the recovered product is in astate suspended in water, but when the modification is performed, it isdispersed in hexadecane as shown in the right of FIG. 13, showing thatthe modification was attained.

The same experiment was carried out for decanal and decane amine, andthe same result was obtained. The state of organically modifiednanoparticles with decane amine is shown on the left of FIG. 13. Itshows that the particles can be surface-modified with a long-chainorganic material hardly soluble to water at about room temperature.

Example 9 (In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (1))

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). Hydrogen peroxide was added to 0.01 Mol/l ofMn(NO₃)₂ aqueous solution to have an amount of 0.05 Mol/l, the resultingmixture 2.5 g was charged in a reactor tube, and hexanol 0.1 cc wasfurther charged therein. The reactor tube was put in a heating furnacepreliminarily set to 400° C., and heated. The pressure is 390 bar on theassumption of pure water. It took 1.5 min to raise the temperature. Thereaction was carried out for 10 min, and the product was recovered. Therecovered product is shown in FIG. 14. In case of using no hexanol, therecovered product is in a state suspended in water as shown in FIG. 14a), and this is caused by generation of hydrophilic groups. In contrast,when the modification was performed, the product was laid in a stateperfectly separated from water phase as shown in FIG. 14b ).

In general, although it is technically difficult to recovernanoparticles generated in an aqueous solution from water phase, theparticles can be easily separated and recovered from the aqueoussolution according to the technique of the present invention. Althoughit is not easy to modify a preliminarily generated metal oxide withhexanol, the organic modification of the oxide nanoparticle surface canbe performed by the in-situ surface modification.

Example 101 (In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (2))

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). Hydrogen peroxide was added to 0.01 Mol/l ofZn(NO₃)₂ aqueous solution to have an amount of 0.05 Mol/l, the resultingmixture 2.5 g was charged in a reactor tube, and hexanol 0.1 cc wasfurther charged therein. The reactor tube was put in a heating furnacepreliminarily set to 400° C., and heated. The pressure is 390 bar on theassumption of pure water. It took 1.5 min to raise the temperature. Thereaction was carried out for 10 min, and the product was recovered. Incase of using no hexanol, the recovered product is in a state suspendedin water, and this is caused by generation of hydrophilic groups. Incontrast, when the modification was performed, the product was laid in astate perfectly separated from water phase. The same experiment wascarried out using Zn(COOH)₂ in addition to Zn(NO₃)₂.

In every case, as shown in Example 4, it was difficult for ZnO toperform satisfactory modification without the coexistence of an acid.According to the present technique, the in-situ surface modification canbe performed. Particularly, in case of a formate, the generated acid isHCOOH, the decomposition of which to H₂+CO₂ in a high temperature fieldis known, and it does not function as the acid. The reason thatsatisfactory surface modification can be attained despite of it isattributable to that the dehydration reaction of hydroxyl group OH withan organic modifying agent in the initial stage of crystal growthsatisfactorily progresses.

TEM images of the particles obtained according to the present techniqueare shown in FIG. 15. It was observed from FIG. 15 that surface-modifiedparticles (the lower side) are uniform fine particles, compared withthose not subjected to surface modification (the upper side). Theparticle growth is inhibited by the surface modification, and fineparticles can be obtained.

Example 11 (In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (3))

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). Hydrogen peroxide was added to 0.01 Mol/l ofMn(NO₃)₂ aqueous solution to have an amount of 0.1 Mol/l, the resultingmixture 2.5 g was charged in a reactor tube, and hexanol 0.1 cc wasfurther charged therein. The reactor tube was put in a heating furnacepreliminarily set to 400° C., and heated. The pressure is 390 bar on theassumption of pure water. It took 1.5 min to raise the temperature. Thereaction was carried out for 10 min, and the product was recovered. Therecovered product is shown in FIG. 16b ). In case of using no hexanol,the recovered product is in a state suspended in water as shown in FIG.16a ), and this is caused by generation of hydrophilic groups. Incontrast, when the modification was performed, the product was laid in astate perfectly separated from water phase.

Example 12 [In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (4)]

An experimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). Hydrogen peroxide was added to 0.01 Mol/1 ofCe(NO₃)₂ aqueous solution to have an amount of 0.01 Mol/l, the resultingmixture 2.5 g was charged in a reactor tube, and hexanoic acid 0.1 ccwas further charged therein. The reactor tube was put in a heatingfurnace preliminarily set to 400° C., and heated. The pressure is 390bar on the assumption of pure water. It took 1.5 min to raise thetemperature. The reaction was carried out for 10 min, and the productwas recovered. The recovered product is shown in FIG. 17. In case ofusing no hexanoic acid, the recovered product is in a state suspended inwater as shown in FIG. 17a ), and this is caused by generation ofhydrophilic groups. Although the treatment was not progressed at 200° C.(FIG. 17b )), the product was laid in a state perfectly separated fromwater phase at 300° C. and 400° C. as shown in FIG. 17 c) and d).

In the modification by use of the hexanoic acid insoluble to water, thetreatment does not progress at a low temperature of 200° C. since ahomogenous layer cannot formed with water, but progresses at 300° C. or400° C., where the dielectric constant of water is reduced to enable theformation of the homogeneous phase with a modifying agent. This showsalso the presence of a case essentially requiring a treatment in ahigh-temperature range where the reaction can sufficiently progress.

Example 13 [In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (5)]

With respect to Fe₃O₃, NiO, ZnO and Co₂O₃, reactions were carried out incoexistence of hexanol, hexanoic acid, hexylamine, hexanal, and hexanethiol in the same manner as Examples 9-12. The results are collectivelyshown in Tables 1-4.

TABLE 1 Fe₂O₃ None R—OH R—CHO R—COOH R—NH₂ R—SH 200° C. W a little, redred little Int. w w w, red thick layer o w, red w, red O more, red 300°C. W red a little red little Int. w o o, red thin layer w, red thicklayer o, red o, brown O more more 400° C. W red a little Int. w w w,brown w, brown thick layer o, brown gray O a little more, red more alittle more L₄₀₀ > L₃₀₀ > L₂₀₀ L₂₀₀ > L₃₀₀ > L₄₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀S₃₀₀ > S₄₀₀ > S₂₀₀ S₃₀₀ > S₄₀₀ > S₂₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₄₀₀ > S₃₀₀ >S₂₀₀ S₃₀₀ > S₄₀₀ > S₂₀₀ NP exist mostly NP exist mostly NP exist mostlyNP are almost NP exist mostly NP exist mostly in in water phase in waterphase in water phase practically in water phase at water phase at at200° C.; in both at 200° C.; and dissolved in 200° C. and 300° C.; 200°C.; and mostly water phase and mostly in organic organic phase at andmostly in boundary phase organic phase phase at 300° C. 200° C.; andexist in organic phase at 400° C., most of at 300° C.; and and at 400°C. mostly in water at 400° C. which are present mostly in organic phaseat 300° C. with organic phase at 400° C. and at 400° C.phase-dependency.

TABLE 2 None R—OH R—CHO R—COOH R—NH₂ R—SH 200° C. W green green a littlea little Int. o o o w w w 0 more, white a little, little little brownwhite white 300° C. W green a little more, green a little Int. o w w w wo 0 little, brown green green more, green 400° C. W a little Int. w,more & w o o o w brown 0 green more, green brown more, black more S₂₀₀ >S₃₀₀ > S₂₀₀ > S₄₀₀ > S₄₀₀ > S₃₀₀ > S₄₀₀ > S₃₀₀ > S₄₀₀ > S₃₀₀ > S₃₀₀ >S₄₀₀ > S₄₀₀ S₃₀₀ S₂₀₀ S₂₀₀ S₂₀₀ S₂₀₀ NP exist NP exist The quantity Thequantity NP almost mostly in mostly in of NP of NP practically waterphase The quantity present present in both exist at 3° C. of NP in bothwater in organic and the present water phase and phase quantity of inboth phase and organic phase at at 300° C. NP present water organic 200°C. is in both phase and phase at smaller water phase organic 200° C.than in and phase at is smaller the cases of organic phase 200° C. isthan in other at 200° C. smaller the cases of temperatures; is smallerthan in other and NP than in the cases of temperatures. exist mostly thecases of other in organic other temperatures. phase temperatures. 400°C.

TABLE 3 ZnO None R—OH R—CHO R—COOH R—NH₂ R—SH 200° C. W more Int. w w w,white w w O more, white more, white a little more, yellow more, whiteyellow 300° C. W Int. w, more o, thin layer o o w, more O yellow yellowmore, yellow white white more, yellow 400° C. W yellow more Int. w,thick layer w, more w, more o, a little o, black O a little white whiteL₄₀₀ > L₂₀₀ > L₃₀₀ L₃₀₀ > L₄₀₀ > L₂₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₃₀₀ > S₂₀₀ >S₄₀₀ S₃₀₀ > S₂₀₀ > S₄₀₀ S₃₀₀ > S₂₀₀ > S₄₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₃₀₀ >S₂₀₀ > S₄₀₀

TABLE 4 CO₂O₃ None R—OH R—CHO R—COOH R—NH₂ R—SH 200° C. W a little, redred red red Int. o o o o o o O gray little, red 300° C. W yellow more,yellow more, yellow more, yellow Int. w w w w, thin layer o O littlemore, gray red 400° C. W more, gray more, yellow yellow yellow more,gray a little Int. w w o w, thin layer o O a little little a little alittle more, gray L₂₀₀ > L₃₀₀ > L₄₀₀ L₂₀₀ > L₃₀₀ > L₄₀₀ L₂₀₀ > L₃₀₀ >L₄₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₂₀₀ > S₃₀₀ > S₄₀₀ S₂₀₀ >S₃₀₀ > S₄₀₀ S₃₀₀ > S₂₀₀ > S₄₀₀ S₄₀₀ > S₃₀₀ > S₂₀₀ The reagent with −NH2Usable as a is excellent at 300° C. satisfactory surface becauseseparation modifying agent is almost perfectly because of highperformed; solubility of NP and the solubility is to this reagent lowerboth in water at 400° C. phase and in organic phase than that in othercases at 400° C.

The respective notations in the tables mean as follows:

None: No modifying agent, W: Water phase, Int.: Interface phase betweenwater phase and organic phase, O: Organic phase, a little: Existing alittle, little: Existing only a little, w: Transferred from interface towater phase by slight vibration, o: Transferred from interface to oilphase by slight vibration, more: Existing more, NP: nanoparticles, L:Thickness of boundary phase with a subscript showing the treatmenttemperature, S: Solubility of NP in organic phase with a subscriptshowing the treatment temperature.

The comparison result as the whole is shown in Table 5.

TABLE 5 Fe₂O₃ 1. At 200° C.: S_(—COOH) > S _(—) _(CHO) > S _(—) _(OH) >S _(—) _(NH2) > S _(—) _(SH) (—COOH is the best reagent) 2. At 300° C.:S_(—CHO) > S _(—) _(OH) > S _(—) _(SH) > S _(—) _(NH2) > S _(—) _(COOH)(—CHO is the best reagent) 3. At 400° C.: S_(—NH2) > S _(—) _(CHO) > S_(—) _(OH) > S _(—) _(SH) > S _(—) _(COOH) NiO 1. At 200° C.: S_(—SH) >S _(—) _(OH) > S _(—) _(COOH) > S _(—) _(CHO) > S _(—) _(NH2) 2. At 300°C.: S_(—SH) > S _(—) _(COOH) > S _(—) _(NH2) > S _(—) _(CHO) > S _(—)_(OH) 3. At 400° C.: S_(—NH2) > S _(—) _(CHO) > S _(—) _(SH) > S _(—)_(OH) > S _(—) _(COOH) ZnO 1. At 200° C.: S_(—NH2) > S _(—) _(OH) > S_(—) _(COOH) > S _(—) _(SH) > S _(—) _(CHO) 2. At 300° C.: S_(—COOH) > S_(—) _(OH) > S _(—) _(CHO) > S _(—) _(SH) > S _(—) _(NH2) 3. At 400° C.:S_(—COOH) > S _(—) _(CHO) > S _(—) _(OH) > S _(—) _(NH2) > S _(—) _(SH)Co₂O₃ 1. At 200° C.: S_(—NH2) > S _(—) _(OH) > S _(—) _(SH) > S _(—)_(CHO) > S _(—) _(COOH) 2. At 300° C.: S_(—NH2) > S _(—) _(CHO) > S _(—)_(SH) > S _(—) _(COOH) > S _(—) _(OH) 3. At 400° C.: S_(—SH) > S _(—)_(NH2) > S _(—) _(COOH) > S _(—) _(CHO) > S _(—) _(OH)

With respect to ZnO, the surface modification treatment can be performedin the same manner. The effect of the surface modification can besufficiently obtained. However, in case of using hexanol, it could notbe said that sufficient surface modification can be obtained in everycase.

Therefore, the in-situ organic modification was carried out. Theexperimental method was the same as in Examples 8 and 9. Namely, theexperimental reaction was carried out using a 5-cc tubular autoclave(tube bomb reactor). Hydrogen peroxide was added to 0.01 Mol/l ofZn(NO₃)₂ aqueous solution to have an amount of 0.1 Mol/l, the resultingmixture 2.5 g was charged in a reactor tube, and hexanol 0.1 cc wasfurther charged therein. The reactor tube was put in a heating furnacepreliminarily set to 200° C., 300° C. and 400° C., and heated. Thepressure is 390 bar on the assumption of pure water. It took 1.5 min toraise the temperature. The reaction was carried out for 10 min, and theproduct was recovered. In case of using no hexanol, the recoveredproduct was in a state suspended in water and oil phase, but theparticles were transferred to the oil phase by the surface modificationusing hexanol. Thus, a sufficient surface modification effect isobtained.

Even if the surface modification cannot be sufficiently performed on theparticles generated once, sufficient surface modification can beperformed by the in-situ surface modification.

The results of the same surface modification treatment of nanoparticlesof ZnO, CeO₂, Al₂O₃, SnO₂, and SiO₂ are collectively shown in Tables 6and 7. Table 6 comparatively shows the result of surface modification ofthe fine particles of each metal oxide, and Table 7 shows the result ofthe in-situ modification thereof. In the tables, o shows that transferof particles to organic phase was recognized, and x shows that transferof particles to organic phase was not clearly recognized. A shows thatthe organic modification progressed although it was insufficient.

TABLE 7 In-situ modification None OH CHO COOH NH₂ SH CeO₂ 200° C. X ◯ ◯X X 300° C. X ◯ ◯ X X 400° C. X ◯ ◯ ◯ ◯ NiO 200° C. ◯ X Δ Δ X ◯ 300° C.X X X ◯ ◯ ◯ 400° C. X X ◯ ◯ ◯ ◯ TiO₂ 200° C. X X ◯ X X X 300° C. X X ◯400° C. X X ◯ ◯ Co₂O₃ 200° C. X X X X ◯ Δ 300° C. X X X X ◯ ◯ 400° C. XX Δ X Δ ◯ ZnO 200° C. X ◯ X ◯ ◯ Δ 300° C. X ◯ ◯ ◯ ◯ ◯ 400° C. X ◯ ◯ ◯ XΔ Fe₂O₃ 200° C. X X X ◯ X X 300° C. X Δ ◯ X Δ ◯ 400° C. X ◯ ◯ X ◯ Δ

TABLE 7 In-situ modification None OH CHO COOH NH₂ SH CeO₂ 200° C. X ◯ ◯X X 300° C. X ◯ ◯ X X 400° C. X ◯ ◯ ◯ ◯ NiO 200° C. ◯ X Δ Δ X ◯ 300° C.X X X ◯ ◯ ◯ 400° C. X X ◯ ◯ ◯ ◯ TiO₂ 200° C. X X ◯ X X X 300° C. X X ◯400° C. X X ◯ ◯ Co₂O₃ 200° C. X X X X ◯ Δ 300° C. X X X X ◯ ◯ 400° C. XX Δ X Δ ◯ ZnO 200° C. X ◯ X ◯ ◯ Δ 300° C. X ◯ ◯ ◯ ◯ ◯ 400° C. X ◯ ◯ ◯ XΔ Fe₂O₃ 200° C. X X X ◯ X X 300° C. X Δ ◯ X Δ ◯ 400° C. X ◯ ◯ X ◯ Δ

As is apparent from the comparison of Tables 1-7, the same in-situsurface modification effect is obtained in ZnO, CeO₂, TiO₂ and the like.

Example 14 [In-Situ Organic Modification in High-Temperature,High-Pressure Hydrothermal Synthesis (6)]

According to the same manner as in Examples 8 and 9, syntheses of Fe₂O₃,Co₂O₃, NiO, ZnO, and TiO₂ were carried out in the coexistence ofhexanol, hexanoic acid, hexylamine, hexanal, and hexane thiol. Theresults are collectively shown in Table 7. Based on the case of using nosurface modifying agent, the magnitude of the surface modificationeffect is expressed by indexes of 1-10.

TABLE 8 —OH —CHO —COOH —NH₂ —SH TiO₂ 200° C. 6 6 1 1 8 300° C. 8 5 4 3 9400° C. 9 8 7 6 10 NiO 200° C. 6 1 1 2 1 300° C. 5 4 5 7 7 400° C. 7 1010 10 8 ZnO 200° C. 3 3 3 3 3 300° C. 6 10 8 4 5 400° C. 7 9 9 5 6 Fe₂O₃200° C. 4 6 8 6 6 300° C. 7 7 7 7 10 400° C. 9 8 5 9 7 Co₂O₃ 200° C. 2 26 7 8 300° C. 2 7 7 7 9 400° C. 2 9 8 6 10

It was found from the table that the degree of progress of the surfacemodification reaction is varied depending on not only the temperaturebut also the reactant. This reason is that even if no surfacemodification is performed, some reactants can be dispersed in waterwhile sufficiently retaining hydrophilic groups as ZnO and NiO, whilesome reactants can be dispersed in oil phase with minimized hydrophobicgroups as TiO₂, and the stability or reactivity of the functional groupon the particle surface is thus varied even if the in-situ surfacemodification is performed in a particle generating field. In case ofmodification with aldehyde or modification with amine, surfacemodification can be obtained more satisfactorily at 300° C. than at 400°C. This is resulted from that a hydrolysis reaction is caused in ahigh-temperature field. Namely, the optimum condition is 300-400° C.,and an excessively high temperature conceivably causes the influence ofthe reverse reaction.

The present invention provides organically modified fine particles(particularly, nanoparticles) having hydrocarbon strongly bonded withthe surface of fine particles, particularly, organically modified metaloxide fine particles, a process for producing the same, and further amethod for recovering or collecting fine particles such asnanoparticles, with an intention to promote the use of nanoparticlesshowing various unique excellent properties, characteristics andfunctions as industrial materials and pharmaceutical and cosmeticmaterials such as ceramic nano-structure modified material, opticalfunctional coating material, electromagnetic shielding material,secondary battery material, fluorescent material, electronic partmaterial, magnetic recording material, and abrasive material.

It will be obvious that the present invention can be executed beyond theabove-mentioned description and examples. In view of the above-mentionedteaching, a lot of alterations and modifications of the presentinvention can be made, and such alterations and modifications aretherefore intended to be embraced by the appended claims.

We claim:
 1. A process for producing organically modified metal oxide nanoparticles, which comprises: reacting an organic modifying agent with the surface of a metal oxide nanoparticle in a reaction field of high-temperature, high-pressure water to form organically modified metal oxide nanoparticles wherein an optionally substituted or unsubstituted hydrocarbon group is bonded to the surface of each nanoparticle through a linkage selected from the group consisting of a covalent bond, an ether bond, an ester bond, a bond through an N atom, a bond through an S atom, a metal-C— bond, a metal-C═ bond, and a metal-(C═O)— bond.
 2. The process according to claim 1, wherein the high-temperature, high-pressure water is water under supercritical or subcritical conditions.
 3. The process according to claim 1, wherein the high-temperature, high-pressure water is water under conditions at the critical pressure or a pressure above the critical point and/or at the critical temperature or a temperature above the critical point.
 4. The process according to claim 1, wherein said organically modified metal oxide nanoparticles are formed in a reaction field where water is present under conditions at a temperature ranging from 250 to 500° C. and a pressure ranging from 10 to 30 MPa.
 5. The process according to claim 1, wherein said hydrocarbon group is a long-chain hydrocarbon group having a chain having 1, 2, 3 or more carbon atoms.
 6. The process according to claim 1, wherein said organic modifying agent is selected from the group other than an alkanethiol.
 7. The process according to claim 1, wherein said organic modifying agent is selected from the group consisting of an alcohol, an aldehyde, a carboxylic acid, an amine, a thiol, an amide, a ketone, an oxime, a phosgene, an enamine, an amino acid, a peptide and a sugar.
 8. The process according to claim 1, wherein said organic modifying agent is selected from the group consisting of an alcohol, an aldehyde, a carboxylic acid, an amine, an amide, a ketone, an oxime, a phosgene, an enamine, an amino acid, a peptide and a sugar.
 9. The process according to claim 1, wherein said metal oxide is an oxide of a metal element selected from the group consisting of elements of the group VIII, elements of the group IB, elements of the group IIB, elements of the group IIIB, elements of the group IVB, elements of the group VB, elements of the group VIB, and elements of the groups IA to VIIA, in the long-period periodic table.
 10. The process according to claim 9, wherein the metal element in said metal oxide is selected from the group consisting of Ti, Zr, Nb, Y, Eu, Mg, Ce, Ba, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, Te and Po.
 11. The process according to claim 9, wherein the metal element in said metal oxide is selected from the group consisting of Ti, Zr, Nb, Y, Eu, Mg, Ce, Ba, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, Te and Po.
 12. The process according to claim 1, wherein said metal oxide is an oxide of a metal element selected from the group consisting of elements of the group VIII, elements of the group IIB, elements of the group IIIB, elements of the group IVB, elements of the group VB, elements of the group VIB, and elements of the groups IA to VIIA, in the long-period periodic table.
 13. The process according to claim 1, wherein the reaction ratio of the organic modifying agent is regulated by controlling a factor selected from the group consisting of temperature, acid concentration and reaction time.
 14. The process according to claim 1, wherein said hydrocarbon group has a hydrophilic group and the products are organically modified metal oxide nanoparticles well dispersed in an aqueous solution.
 15. The process according to claim 1, wherein the average size of the nanoparticles is: (1) 100 nm or less; (2) 50 nm or less; (3) 20 nm or less; (4) 10 nm or less; or (5) 5 nm or less.
 16. The process according to claim 1, wherein the particle size of the generated particles is adjusted to a smaller particle size as compared with those where supercritical hydrothermal synthesis is performed in the absence of an organic modifying agent.
 17. The process according to claim 1, wherein said hydrocarbon group has a hydrophobic group and said organically modified metal oxide nanoparticles are well dispersible in an organic solvent phase, or can be transferred to the interface between an aqueous phase and an organic solvent phase.
 18. The process according to claim 1, wherein said metal oxide is selected from the group consisting of SiO₂, SnO₂, Al₂O₃, MnO₂, NiO, Eu₂O₃, Y₂O₃, Nb₂O₃, InO, ZnO, Fe₂O₃, Fe₃O₄, Co₃O₄, ZrO₂, CeO₂, BaO.6Fe₂O₃, Al₅(Y+Tb)₃O₁₂, BaTiO₃, LiCoO₂, LiMn₂O₄, K₂O.6Ti O₂ and AlOOH.
 19. The process according to claim 1, wherein said metal oxide is selected from the group consisting of SiO₂, Al₂O₃, MnO₂, ZnO, CeO₂, Fe₂O₃, Fe₃O₄, NiO, Co₂O₃, Co₃O₄, SnO₂, Y₂O₃, InO, MgO, Nb₂O₅, Nb₂O₃ and ZrO₂.
 20. The process according to claim 1, wherein the particle size of product particles is evaluated by transmission electron microscopic (TEM) analysis.
 21. The process according to claim 1, wherein the state of bonding a substituted or unsubstituted hydrocarbon group to the surface of a metal oxide nanoparticle is verified by IR analysis and/or thermogravimetric analysis.
 22. The process according to claim 1, wherein said hydrocarbon group is a hydrocarbon group with a long-chain hydrocarbon group with a chain having 4 or more carbon atoms.
 23. A process for producing organically modified metal oxide nanoparticles, which comprises: reacting an organic modifying agent with the surface of a metal oxide nanoparticle in a reaction field of high-temperature, high-pressure water to form organically modified metal oxide nanoparticles wherein an optionally substituted or unsubstituted hydrocarbon group is directly bonded to a surface of each metal oxide nanoparticle through a linkage from the hydrocarbon group selected from the group consisting of a covalent bond, an ether bond, an ester bond, a bond through an N atom, a bond through an S atom, a metal-C— bond, a metal-C═ bond, and a metal-(C—O)— bond, and said metal oxide is an oxide of a metal element selected from group consisting of an element of group VIII, an element of group IB, an element of group IIB, an element of group IIIB, an element of group IVB, an element of group VB, an element of group VIB, and an element of groups IA to VIIA, in the long-period periodic table, wherein the hydrocarbon group is strongly bonded to the surface of said metal oxide nanoparticle.
 24. The process according to claim 23, wherein said hydrocarbon group is a hydrocarbon group with a chain having 1, 2 or 3 carbon atoms, or a long-chain hydrocarbon group with a chain having 4 or more carbon atoms, or said hydrocarbon group is a substituted or unsubstituted straight-chain or branched-chain alkyl group.
 25. The process according to claim 23, wherein the metal element in said metal oxide is selected from the group consisting of Ti, Zr, Nb, Y, Eu, Mg, Ce, Ba, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Te and Po. 